Exposure to the ultraviolet radiation from the sun has the potential to cause significant damage to the body including skin irritation, burning, and skin cancer. It has become a very common practice to use UV blocking lotions and creams to minimize the damage from sun exposure. While the general population is well aware of the potential for damage to skin from UV radiation, there is less awareness of the possibility of damage to other organs, particularly eyes. There is a growing concern that continuous exposure of UV radiation to eyes could cause serious medical problems including cataract and retina damage. UV radiation can cause mild irritation and a foreign body sensation in the eyes. Regular UV exposure can cause blindness, cataracts, photokeratitis, erythema of the eyelid, solar retinopathy, retinal damage, and cancer of cornea or conjunctiva. Damage from the UV radiation is likely due to free radical formation that causes protein modification and lipid peroxidation. The intraocular lens of an adult eye filters a majority of the UV light, whereas the lens of an infant's eye transmits nearly all of the UV light. UV transmittance decreases with age, and by the age of 25 nearly all UV light is absorbed by the lens. Accumulated exposure to UV light by the age of 25 could cause significant retinal damage.
UV damage can be minimized by wearing eye glasses or contact lenses that are protective against peripheral radiation. The degree of blocking however depends on the type of lenses and the design of the sunglasses. Most styles of sunglasses do not offer complete protection from UV radiation, allowing UV light to reach the eyes around the frames of the eyeglasses. Wearing UV blocking contact lenses, which cover the entire cornea, can provide UV protection from all angles.
The U.S. Food and Drug administration (FDA) has established standards for UV blocking contact lenses based on American National Standards Institute (ANSI) standards, and classifies UV blocking contact lenses into two categories (Class 1 and Class 2) depending on the extent of the protection. Class 1 lenses must block more than 90% of UVA and 99% of UVB (280-315 nm) radiation. Class 2 lenses must block more than 70% of UVA and 95% of UVB radiation. Although UVA radiation corresponds to the wavelength range of 315-400 nm, only wavelengths from 315-380 nm are considered for classification of a contact lens. Only three commercial contact lenses (ACUVUE® Oasys™, ACUVUE® Advance® and ACUVUE® Advance for Astigmatism) are categorized as Class 1 blocking lenses.
UV blocking by contact lenses is achieved by adding a UV absorbing molecule to the lens composition. UV absorbers and the preparation of UV blocking contact lenses has primarily involved monomeric UV absorbers that contain an acrylic or styrenic group for copolymerization with the lens forming material, for example: Loshaek, U.S. Pat. No. Re. 33,477; Dunks et al., U.S. Pat. No. 4,716,234; Bambury et al., U.S. Pat. No. 4,719,248; Jinkerson, U.S. Pat. No. 5,470,932; Jinkerson, U.S. Pat. No. 5,543,504; Collins et al., U.S. Pat. No. 5,637,726; Haywood et al., U.S. Pat. No. 7,364,291; and Jinkerson et al., U.S. Pat. No. 7,803,359. Hong et al., U.S. Pat. No. 6,914,086 teaches a crosslinkable UV absorber with a plurality of polymerizable vinyl groups for incorporation by copolymerization with the lens forming material. Hung et al., U.S. Pat. No. 4,963,160 teaches the absorption of an acid salt comprising an absorber on a contact lens followed by neutralization and extraction until only surface bound UV absorbers remain on the lenses. Fabrication of UV absorber containing contact lenses, or the contact lenses themselves, often suffer from one or more undesired features such as: long reacting times; low conversions; uncertainty in the degree of reaction; leach of unreacted UV absorber; yellowness; inconsistent integrity of the formed lens; expensive reactants; and tedious reacting process.
The major challenges in preparing a contact lens loaded with a UV absorber remain preparing the lens with short curing times at reasonable light intensities to avoid any undesired side reactions, maintaining the clarity and uniformity of the lens and the Absorber over the entire area of the lens, and avoiding any leaching of UV absorber from the lens. As currently there are only a few commercially available contact lenses that are approved as Class 1 UV blockers, there remains a need to develop effective UV blocking contact lenses.